This invention pertains to bleaching gels for use in bleaching teeth. More specifically, this invention relates to substantially anhydrous dental bleaching gels that contain: (i) at least 25% by weight organic polyol; (ii) less than 3% by weight polyacrylic acid thickening agent; (iii) at least 10% by weight carbamide peroxide (or a chemically equivalent amount of another bleaching agent, such as 3% by weight hydrogen peroxide); (iv) neutralizing agent; (v) chelating agents; (vi) desensitizing agent; and (vii) flavorants.
A gel is a colloid produced by combining a dispersed phase with a continuous phase (i.e., a dispersion medium or matrix) to produce a viscous, jelly-like, semisolid material. In the dental industry, gels are utilized as vehicles for applying a variety of dentifrices, bleaching aids, and fluoride compounds to teeth. A xe2x80x9cdental bleaching gelxe2x80x9d is a gel that carries a bleaching agent that can be safely applied to teeth.
The thickening agent or gelling agent utilized to form the continuous phase of most dental bleaching gels is selected from carboxymethylcellulose, xanthan gum, carrageenan gum, nonionic surfactants, polyethylene oxide macropolymers such as Polymer H(copyright), and carbomers such as Carbopol(copyright) 940. The dispersed phase of most dental bleaching gels is water and/or an organic polyol such as glycerine. The bleaching agents of choice tend to be hydrogen peroxide (H2O2), or compounds, such as urea peroxide (CO(NH2)2H2O2), that yield hydrogen peroxide in an aqueous environment (such as the mouth).
For example, U.S. Pat. Nos. 5,098,303, 5,234,342, 5,376,006, and 5,725,843, assigned to Ultradent Products, teach water-based bleaching gels that contain 3.5% or more Carbopol(copyright) 934P or 940 carbomer, glycerine, and a peroxide such as hydrogen peroxide or carbamide peroxide (urea peroxide). In addition, PROXIGEL(copyright), described in U.S. Pat. No. 3,657,413, is a teeth whitening composition that contains urea peroxide. Finally, Den-Mat Corporation currently sells a dental bleaching gel composition called LIGHTEN GEL that is a glycerine composition containing carbamide peroxide and Carbopol(copyright) 940 carbomer in an amount ranging from 0.6 to 11 weight percent.
The dental bleaching agents described above are all effective for whitening teeth. However, the use of bleaching agents such as urea peroxide serves to aggravate hypersensitive teeth and causes a period of discomfort. It would be desirable to develop an improved bleaching agent that is equally effective in whitening teeth and reducing or eliminating the dental hypersensitivity sometimes aggravated by bleaching agents.
There is also an ever present need in the art to develop dental bleaching agents that can be more easily and quickly processed, that employ lesser amounts of thickening agent, and that exhibit superior gel stability. Such gels would be more commercially viable.
This invention relates to substantially anhydrous dental bleaching gels that contain: (i) at least 25% by weight organic polyol; (ii) less than 3% by weight polyacrylic acid thickening agent; (iii) at least 10% by weight carbamide peroxide (or a chemically equivalent amount of another bleaching agent, such as 3% by weight hydrogen peroxide); (iv) a neutralizing agent; (v) a desensitizing agent; (vi) chelating agents; and (vii) miscellaneous materials such as Citroxain(copyright) and flavorants. Preferably, the desensitizing agent is an alkali or alkaline earth metal salt of an organic or inorganic acid or halide such as potassium nitrate, potassium citrate, strontium nitrate and strontium chloride. The thickening agent is chosen so that even in low amounts it will produce a gel with a desired viscosity. The gel can be processed in an easier and faster fashion and exhibits higher stability. These and other features and advantages of the invention are described in, or are apparent from, the following detailed description of the preferred embodiments. Gels made as described above, but without a chelating agent, will (at higher peroxided concentrations) exhibit instability resulting in release of oxygen gas that can cause packaging leaks.